1. Technical Field
The present invention relates to a light emitting device using an organic electroluminescence element as a light emitting element.
2. Related Art
Recently, as a light emitting device that is used in a display screen of a cellular phone, a personal computer, or the like, an organic EL device that forms an image by regularly arranging organic electroluminescence (hereinafter, referred to as organic EL) elements as light emitting elements on a display surface that is a surface on a side for outputting light has been considered.
Each light emitting element has a function layer that includes at least a light emitting layer (organic EL layer) between an anode and a cathode that are formed to face each other, and light is emitted by a current flowing between the anode and the cathode. The organic EL device forms an image by outputting the emitted light from the display surface. In addition, a configuration in which a reflective layer is disposed on a side opposite to the display surface and the emitted light is effectively used by reflecting light to the display surface side is generally used. To the above-described configuration, a configuration in which an electrode located on the display surface side is formed of a material having semi-transmissive reflectivity and light in a target wavelength range is enhanced and output by forming a microcavity structure between the reflective layer and the electrode is frequently added.
In the organic EL device having such a configuration, reflection of external light may be a problem. Since the reflective layer reflects not only the emitted light but also external light incident from the display surface, the reflected external light is mixed in the emitted light in a bright place, and thereby contrast may be degraded.
As means for decreasing reflection of external light, a configuration in which a circular polarizing plate is bonded to the display surface side has been proposed (see JP-A-9-127885). Under the configuration, output of the reflected light from the display surface is suppressed by using a property that the direction of rotation of light modulated by the circular polarizing plate is reversed by reflection, and thereby contrast is improved.
In addition, when the organic EL device is a color image display device, a configuration in which a color filter is used has been proposed. By disposing color filters that transmit light of a wavelength range of emitted light and absorb light having wavelengths out of the wavelength range to light emitting elements of a total of three types including a red light emitting element that emits red light, a green light emitting element that emits green light, and a blue light emitting element that emits blue light, reflection of external light having wavelengths out of the wavelength range of emitted light can be decreased.
However, there are following problems in the above-described techniques. First, in the technique using the circular polarizing plate, a component polarized in one direction of the emitted light is absorbed, and thus, the ratio of light output from the display surface becomes a half or less, and accordingly, luminance decreases. When a current flowing through the light emitting layer is increased so as to supplement the decrease in the luminance, power consumption increases, or the lifetime of the light emitting layer may be shortened.
In addition, in the technique using the color filters, external light having wavelengths within the wavelength range of the light emitted by the light emitting elements cannot be absorbed, and accordingly, the reflection of external light cannot be sufficiently decreased.
In addition, in any of the above-described techniques, the same reflection decreasing means is provided for all the light emitting elements of the three types, and the spectral luminous efficacy (degree of spectral luminous effect) is not considered. Accordingly, there is a problem that the decrease in reflection of external light may be insufficient depending on the types of the light emitting elements.